In audio and voice processing technologies, a bandwidth expansion technology already emerges, that is, a high-frequency band signal is encoded using a small number of bits so as to expand a frequency band range of a voice/audio signal. The bandwidth expansion technology has developed fast in recent years and has been commercially applied in some encoders and decoders.
The bandwidth expansion technology adopted currently is basically a multi-mode bandwidth expansion technology, where according to signal characteristics of a high-frequency band signal in an input signal, a signal class of the high-frequency band signal is determined, and different encoding and decoding algorithms are adopted for different signal classes. According to signal characteristics of high-frequency band signals, the high-frequency band signals are classified into four classes: a transient (Transient) class, a harmonic class (Harmonic), a noise (Noise) class and a normal (Normal) class. A specific classification process includes: dividing a high-frequency band time-domain signal of a certain frame into several sub-frames, obtaining a time-domain envelope of each sub-frame, and when energy of a certain sub-frame is greater than a certain number of times of energy of a previous sub-frame and the energy of the sub-frame is greater than a certain number of times of average energy of all sub-frames in the whole frame, determining that the high-frequency band signal of the frame is of the transient class; if the frame is not of the transient class, dividing a high-frequency band frequency-domain signal of the frame into several sub-bands, obtaining a peak-to-average ratio of each sub-band, where the peak-to-average ratio is a ratio of peak energy or amplitude of the sub-band to average energy or amplitude of the sub-band, and when the number of sub-bands having a peak-to-average ratio greater than a threshold is greater than a certain number, determining that the high-frequency band signal of the frame is of the harmonic class; when the number of sub-bands having a peak-to-average ratio smaller than a threshold is greater than a certain number, determining that the high-frequency band signal of the frame is noise; otherwise, determining that the high-frequency band signal of the frame is of the normal class.
The prior art has the following disadvantages.
In the prior art, during signal classification for a high-frequency band signal of a certain frame, only characteristics of the high-frequency band signal of the frame are considered, which results in an inaccurate signal classification result for the high-frequency band signal of the frame.